Method and apparatus for moving a shaft into a predetermined angular position

ABSTRACT

A method and apparatus through which a moving shaft is stopped in a predetermined angular position. The shaft is driven at a maximum speed through an electrically driven motor. When the shaft is to be stopped at the predetermined angular position, the shaft is decoupled from the motor and an electromagnetic brake is applied. A regulating circuit controls the braking action so that it is dependent on a comparison of the actual output speed of the shaft and a desired input speed, as well as the comparison of a computed braking angle and the predetermined angular position to which the shaft is to be rotated. Position and speed sensors connected to the shaft provide signals representing the instantaneous output position and speed of the shaft.

United States Patent 1191 Daab Sept. 25, 1973 [54] METHOD AND APPARATUSFOR MOVING 3,226,621 l2/l965 Heinemann et al 318/369 x A SHAFT INTO APREDETERMINED ANGULAR POSITION 2:753:502 7/1956 318/369 X [75] Inventor:Heinz Daab, Darmstadt-Arheilgen, 3,582, 6/l 8/467 X Germany 3,659,1724/1972 Kuniaki et al. 318/467 [73] Asslgl'eez gzifr gg gxgg & Not:Primary ExaminerT. E. Lynch y AtlrneyMichael S. Striker [22 Filed: Nov.4, 1971 [21] Appl. No.: 195,757 [57] ABSTRACT A method and apparatusthrough which a moving shaft [30] F i Application priority Data issftopped in a predetermined angular position. The

ha t is driven at a maximum s eed throu h an electri- N 5.1970 o..P205450l.l S P g m ermany cally driven motor. When the shaft is to bestopped at [52] US CL 318/467 318/369 318/372 the predetermined angularposition, the shaft is decou- {12/219 pled from the motor and anelectromagnetic brake is {51] Int Cl 02p 3/00 applied. A regulatingcircuit controls the braking ac- [58] Field tion so that it is dependenton a comparison of the ac- 1 12/219 tual output speed ofthe shaft and adesired input speed, as well as the comparison of a computed brakingangle [56] References Cited and the predetermined angular position towhich the shaft is'to be rotated. Position and speed sensors con- UNITEDSTATES PATENTS nected to the shaft provide signals representing the inistantaneous output position and speed of the shaft. rcn emue t 3,125,0503/1964 Bertrand 3l8/467 X 27 Claims, 14 Drawing Figures 2 3 5 94 6 w 3 7I M0702? I I mvawm I 76 i [I I pas 770 I I COMPA'RHTfl/p 8 I 9" l v l 1114/ 1 OUT/ 07' l $1 550 x 55/1/50? u/7 CQ/WPUT/NC /9916470? PEGUL/If/A/GC/pawr C/ACW/f M6 07 73 SPEED S/G/Vfll.

PATENTEDSEPZSISU SHEET 4 0F 6 IN VEN TOR BYv BJSIJSO PATENIEDSEPZS'QTSSHEET 6 BF 6 IN V EN TOR METHOD AND APPARATUS FOR MOVING 'A SHAFT INTO APREDETERMINED ANGULAR POSITION BACKGROUND OF THE INVENTION The presentinvention relates to a method and apparatus for positioning a shaft intoa predetermined angular location by using an electrical motor with anelectrically-operated coupling. The coupling connects the shaft to bepositioned with the motor for purposes of imparting to the shaft apredetermined operating speed. The coupling, as well as a brake windingthrough which the shaft is braked into the desired end position, areenergized and controlled through a regulating circuit.

Conventional position control arrangements of the preceding speciesoperate, in general on the basis that when the shaft is to bepositioned, it is first braked to a lower speed from its higheroperating speed and then a regulator maintains the lower speed of theshaft until a synchronizer becomes actuated or becomes operative forapplying the final braking action to bring the shaft to a stop position,whereby the speed is then reduced to zero. The stopping process for theshaft under this conventional method, is not a continuous process. Instead, the conventional procedure is a stepwise control withintermediate delay periods in the lower operating speed portion of thecycle. The time interval during which the shaft to be positioned,operates at the lower braked speed, is dependent upon the angularposition which the operating shaft is to assume upon reaching the lowerbraked speed, and thus this time interval can be greater or smaller.This time interval can, in fact, attain a value which corresponds to afull revolution of the operating shaft when rotating at the lower brakedspeed.

In many applications, as for example, in driving of industrial sewingmachines, it is essential to position the shaft not only with highaccuracy and precision, but also to carry out the positioning procedurewithin the shortest possible time. This requirement may be understoodwhen taking into account the condition that industrial sewing machinesare switched daily approximately ten thousand times. Accordingly, even aslight shortening of the period of time during which the shaft isstopped in a desired position, will have a considerable influence uponthe productivity of the machine.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a positioning arrangement in which a rotatableshaft is positioned to a predetermined angular position within asubstantially short time.

It is also an object of the present invention to position a rotatableshaft, as set forth, with substantial accuracy and precision.

It is a still further object of the present invention to provide apositioning arrangement of the foregoing character which is simple indesign and may be readily fabricated.

Another object of the present invention is to provide a shaftpositioning arrangement which has a long operating life and may bereadily maintained.

The objects of the present invention are achieved by providing a methodunder which the actual output speed of the shaft to be positioned iscontinuously measured. A braking torque is applied which is lower thanthe maximum applicable braking torque, as computed in correspondence toa required braking angle which is related to the actual output positionof the shaft. The actual output position of the shaft is measuredinstantaneously and compared with the computed braking angle. The signalobtained from the comparison of the angular positions, as applied to theregulator which also is controlled through a speed comparison whichcompares a desired input speed of the shaft with the actual output speedof the shaft. The regulator then provides signals by which the shaft ispositioned into the desired angular location. In accordance with themethod of the present invention, the time interval delay incurred withthe lower braking speed used in the conventional methods is avoided. Theoperating shaft is braked, in accordance with the present invention tozero velocity in one predetermined procedural step which applies apredetermined braking function. The halting procedure of the shaft isregulated and this is also not found in the conventional methods. In thelatter, there is no regulation after braking to the lower speed andallowing the synchronizer to become operative. In conjunction withshortening the time interval by which the shaft is positioned,therefore, the shaft is also positioned with c0nsiderably greateraccuracy and precision, in accordance with the present invention, andtherefore considerable improvement is obtained over the prior art.

In a further embodiment of the present invention the brake can be fullyapplied when the procedure for stopping the shaft is initiated. Thebrake can then be partially applied until the desired braking angle isattained. The braking action, in such case, is applied with full forcein order to obtain a speed versus angle function which passes throughzero, whereby no time is spent during an intermediate speed incorrespondence to the conventional lower speed interval. If the functionduring the regulated braking interval is denoted by w f (n), and if theequation describing the functional operation for the unregulated part ofthe process is denoted by w =f (n), then the switching from anuncontrolled procedure to the controlled procedure takes placepreferably at the intersection of these two functions, where w is thebraking angle dependent upon the predetermined angular shaft position,and n is the actual output shaft speed.

The actual output shaft speed can be obtained from variations in thespeed of the angle measuring sensor. It is also possible, instead, toderive the value for the angular position from the actual speedparameter. For this purpose, pulses from a speed measurement may besummed from a speed output generator.

The output signal of the comparator which compares the braking functionangle with the actual position of the shaft is preferably connected to aregulator which also takes into account the actual output shaft speedand the desired input shaft speed for the purpose of generating aregulating signal for purposes of bringing the shaft to the desiredstationary position. For the rapid initial braking mentioned above,which is applied prior to carrying out regulation as a function ofangular position, a gate is connected to the sensor which determines theactual output speed of the shaft for inhibiting the transmission of theoutput from the computing device for as long as the actual shaft outputspeed is above a predetermined value. Until this value is obtained, thebraking action takes place exclusively on the basis of u comparison ofthe actual output speed of the shaft with a desired input speed.

While operating with a desired input speed generator which has a presetoperating speed, it is possible to prevent undesired positioning of theshaft through the use of a gate connected to this generator for applyinga desired input speed to the shaft. This gate causes to preventtransmission from the output of the computer which computes the brakingfunction and applies it to a comparator for comparing against the actualoutput angular position of the shaft. The gate serves to block theoutput of this comparator for as long as the preset desired input speedis different from zero. First when the desired input speed generator isset to zero for the purpose of retaining the operating shaft in apredetermined angular position, does the gate permit the transmission ofthe output from the comparator which has the computing function as oneinput and the actual position of the shaft as the second input.

The regulator can have connected before it a control stage which causesthe control windings for the motor coupling to be deenergized as afunction of reaching the desired input position for the shaft. With thisarrangement, the operating shaft becomes then freely rotatable afterhaving reached its desired, predetermined angular position, and canthen, as desired, be rotated by, for example, hand.

When braking as a function of angular position, in accordance with thepresent invention, it is particularly important to obtain precisely theinstantaneous angular output position of the shaft until substantiallyvery low speeds for the shaft are obtained. In order to meet theseconditions, an angular measuring device with a hall generator is used.The latter becomes influenced through a magnetic disc coupled to theoperating shaft. This magnetic disc has a continously decreasing radiusfrom a maximum value to a minimum value. A sudden step takes place fromthe transition of the minimum value to the maximum value, Such anangular measuring sensor or device ir independent of frequency andspeed. As a result, angular positions can be precisely reproduced andmeasured even at low speeds for the shaft. In addition, this angularposition sensor, in accordance with the present invention, has nocontacts, and this results in substantially high operating reliabilityand long operating life of the unit. The sudden step in the magneticdisc profile can be used, in a simple manner, for marking the desiredinput angle of the operating shaft. In this manner, the angular positionsensor fulfills the function of a sensor for determining the actualoutput shaft angular position and as a generator for providing thedesired input angle.

In place of the actual speed sensor for determining the output shaftspeed, it is possible to use basically any of theconventional sensingdevices, as for example, a tachogenerator which provides a voltage as afunction of speed, or a pulse train which has a pulse frequencydependent'upon the shaft speed. In accordance with a further embodimentof the present invention, the hall generator for measuring angularposition can also be used for providing speed measurements. In such anarrangement, the actual output shaft speed is provided through acomputing device which computes the speed from the measured angularposition. Since the speed is the time derivative of angular position,the actual output speed can be obtained basically from the actual outputangle, through the computing device which may be designed in the form ofa differentiating stage. Such a differentiating stage is well known inthe art and can be of varied' construction. A direct differentiation,however, can lead to instabilities in the regulating system. Suchinstabilities may be avoided when, in accordance with a furtherembodiment of the present invention, the actual shaft output speed andthe actual shaft angular position from which the speed is determinedthrough a computing device, are connected to two operational amplifiers.The first of these operational amplifiers is in the form of a summingamplifier, whereas the second amplifier is constructed in the form of anintegrator with feedback coupling so that when an input voltage of x(t)is applied, the output of the summing amplifier provides a voltage inthe form of y(r) x by J' y dr. In this relationship, b is different fromone, and the integrator becomes reset at the completion of eachrevolution.

The computing dwvice for the braking function is provided preferablywith an operational amplifier having a feedback network, so that when aninput voltage x(t) is applied to the amplifier, the latter provides anoutput voltage of the form y(t) e C.

The comparator for comparing the braking function with the actual outputshaft angle, as well as the second comparator can be advantageouslydesigned in the form of summing amplifiers. Operational amplifiers ofsuch design can be constructed from low cost miniature components havinghigh precision.

In practice, it is often necessary to move the operating shaft into asecond desired position after having held it in a first desiredposition. The second position of the shaft may be separated by less than360 from the first stopping position. The present invention provides forthis feature by providing a control device which is influenced by theinput angle position generator, whereby the regulator receives a controlsignal after the operating shaft has been stopped in the first desiredposition. This control signal then causes the operating shaft to furtherrotate into a second position. For this arrangement, it is desirable toalternatingly block the transmission of the output of the comparator forthe brake function and actual shaft angular position, as well as theoutput for the control circuit associated with the secondstopping-position of the shaft. Programming stages are preferablyprovided through which the components used in the preceding arrangementcan be controlled, so that the stopping of the shaft in the seconddesired position is always preceded by a braking of the shaft to thefirst desired position.

The transfer from the first position to the second shaft position can becarried out through any desired one of a number of possible circuits. Aparticularly simple operating circuit is made possible by providing thatby means of the desired input speed generator, the command signal forthe transfer from the first position to the second position is alsoobtained. In such a case, it is advantageous to provide a gate betweenthe desired input speed generator and the regulator. The gate preventsthe infiuence of the regulator through the output signal from thedesired input speed generator during rotation of the operating shaftfrom the first position into the second desired position.

The precision of angular measurement carried out through the use of theaforementioned hall generator can be considerably increased through theuse of comparator stages which compare the minimum and maximum valuesfrom the hall generator with reference voltages. In conjunction withthis arrangement relating elements are provided which apply regulatingfunctions in dependent on the reference values as a function of.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a block diagram and shows thecontrolling arrangement for positioning a shaft, in accordance with thepresent invention;

FIG. 2 is a block diagram of a second embodiment of the arrangement ofFIG. 1;

FIG. 3,is a schematic diagram of a third embodiment of the presentinvention;

7 FIG. 4 is a schematic diagram of a computing circuit for computing abraking function used in conjunction with the arrangement of the presentinvention;

FIG. 5 is a circuit diagram for a preferred embodiment of the computingcurcuit of FIG. 4;

FIG. 6 is a functional schematic diagram of an arrangement for derivinga speed signal from an angular position signal to be used in conjunctionwith the arrangement of the present invention;

FIG. 7 is a circuit diagram for the arrangement of FIG. 6;

FIG. 8 is a sectional elevational view of a preferred angular positionsensor, in accordance with the present invention;

FIG. 9 is a plan view of a magnetic element used in the sensor of FIG.8;

FIG. 10 is an enlarged sectional view of an angular measuring devicetaken along line XX in FIG. 11;

FIG. 11 is a partial sectional view taken along line XI-XI in FIG. 10;

FIG. 12 is an enlarged view of the measuring head used in the angularmeasuring device illustrated in FIGS. 8 to 11, when viewed from below;

FIG. 13 is a graphical representation of the waveform of the signalprovided by the angular measuring device used in FIGS. 8 to 12 formeasuring an actual shaft position; and

FIG. 14 is a circuit diagram for stabilizing the arrangement using theangular measuring device shown in FIGS. 8 to 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, thebrake characteristics of a motorized or motor-driven coupling aregenerally known in the art, or they may be determined empirically in asimple manner. In general, motor-driven coupling arrangements operate ina manner that when a constant voltage is applied to the brake winding ofthe coupling, a constant braking torque is applied to the driven shaft.

If the angular rotation of the driven shaft is denoted by ,w, and therotational speed of a shaft is denoted by n, then for the mass m of theshaft the braking torque is given by Since the mass m is constant, thenfor a constant braking torque M dn/dt const.

Since, moreover n 141 n dt -j dn (in It follows from a combination ofequations 2 and 3 that Equation 4 illustrates that a quadraticrelationship prevails between the angular rotation of the brake shaftand the speed of the shaft when the applied braking torque is constant.Consequently, provided that the braking torque remains constant, then apredetermined angle of rotation of the brake shaft can be associated foreach value of shaft speed, through the quadratic relationship.

It will be understood, of course, that a relationship can also bederived when the applied braking torque is not constant. For purposes ofsimplicity, however, it will be assumed that the braking torque isconstant in the following analysis and application. This assumptionsimplifies the analysis.

The principle of the present invention involves the use of a computingelement which takes into account the known braking characteristics of amotor driven coupling, and computes the braking angle or rotationalangle of the shaft for the corresponding speed of the shaft. Afterhaving computed the angular rotation of the driven shaft to be braked,this computed angle is compared with an instantaneously measuredposition of the shaft, and the comparison is used to generate aregulating signal or parameter by which the braking coils for the shaftand/or coupling windings are energized, in order to produce the desiredend results. Such end result is achieved by forcing the braked shaft tobecome stopped in an angular position which corresponds to the anglecomputed by the computing element. The movement of the shaft towardsthis desired computed angle is continuously monitored until the shafthas obtained this predetermined computed position. As a result, of theuse of this arrangement, it is theoretically possible to obtainunlimited high precision for positioning the shaft. In practice, theprecision for positioning a shaft, in this manner, is only limitedthrough the component parts which are used, particularly the angletransducer which is the element that senses the instantaneous angularposition of the shaft to be braked. The design of the computing elementfor the braking function is not to be based upon the maximum applicablebraking torque. Instead, the design is to be based on a braking torquewhich permits regulation with an applied torque which is also below thatof the maximum applicable torque. In carrying out the braking process,furthermore, no regulating deviations are to prevail which will requirean instantaneous increase in the applied braking torque.

FIG. 1 shows in schematic form, a positioning arrangement, in accordancewith the present invention. The motor 1 which drives the coupling has acontinuous maximum rotational speed applied to its rotating shaft 2,which, in turn, carries a driving disc 3. A driven shaft 4 carries acoupling disc 5 and a driving pulley 6. By actuating a coupling winding7, the coupling disc 5 can be made to move into contact with the drivingdisc 3. When energizing the braking winding 8, on the other hand, thecoupling disc 5 is brought to bear or press against a braking member 9.Motorized drives of this type of construction are also known in the art,which have a subdivided coupling disc. Such subdivided coupling discmakes it possible to simultaneously engage the driven shaft with thedriving disc and the braking member with more or less pressure. Thewindings 7 and 8 are controlled through a regulating circuit 10.

' A rotational speed sensing device 11 determines continuously theinstantaneous rotational speed of the driven shaft 4. Through theapplication of an input speed signal generator 12, the desired inputspeed of the driven shaft 4 may be adjusted or set. The signals from thespeed sensor 11 and the input speed signal generator 12 are compared ina comparator 13. The difference between the two signals being compared,is applied in signal form to the regulating circuit 10. The arrangementdescribed up to this point, is known in the art, and operates in themanner so that the regulating circuit provides regulation whereby thedriven shaft is caused to operate at a speed corresponding to the inputspeed determined by the generator 12.

In accordance with the present invention, the output speed sensingdevice 11 is connected to a computing circuit 14, which computes thebraking angle or angle of rotation of the shaft corresponding to theinstantaneous speed of the shaft, as measured by the sensor 11. Thisbraking angle or angle of rotation of the shaft represents the anglethrough which the shaft will rotate to become stationary upon theapplication of a torque which is less than the required maximum brakingtorque. The computing circuit 14 can be designed, for example, so thatthe applied braking torque corresponds to a predetermined level ofexcitation of the braking winding 8. The output signal from thecomputing circuit 14 is applied to a comparator 16 which has also asecond input derived from an angle transducer 15. This angle transducermeasures angular position of a shaft or change in that position. Theangular position sensor 15 measures continuously the angle which thedriven shaft must pass through in order to attain the desired positionat which the shaft is to be stopped. This measured output angularposition derived from the sensor 15 is compared with the desired inputangle as computed by the circuit 14. The computing circuit 14 providesthe desired input or positioning the shaft, in accordance with therequired braking angle corresponding to the prevailing rotational speedof the shaft to be positioned. The output signal from the comparator 16is also'applied to an input of the comparator 13.

In operation of the circuit arrangement of FIG. I, the input speedsignal generator 12 is set to zero, when the shaft is in the desiredposition. The circuit elements 14, 15 and 16 are simultaneously set intooperation. For

this purpose a gate, not shown, can be connected between the output ofthe comparator l6 and the corresponding input to the comparator 13, soas to gate as desired, the signal from the comparator 16 to thecomparator 13. The deviation of the input speed signal generator fromthe output speed sensor is adjusted so as to become zero. The regulator10 has then a signal applied to it by the comparator 13, so as toenergize the brake winding 8. As a result of this action, strong brakingof the driven shaft 4 results, as well as of any shaft connected to thisdriven shaft. The closer the instantaneous measured speed of the shaftis to the desired and set input speed, and this set input speed is zero,the stronger is the influence of the output signal on the comparator 16on the regulator 10. As a result, the drive shaft is brought to theposition computed by the circuit 14, and the shaft is braked by theregulator 10 in correspondence with a predetermined braking function.Such braking action applied by the regulating circuit 10 takes placeuntil the output signals from the circuit 11, 12 and those from theelements l4, 15 are all equal, whereby the output from the comparator 13is zero.

FIG. 2 shows in schematic form another embodiment of the arrangement ofFIG. 1. From the viewpoint of simplifying the diagram, only the windings7 and 8 are shown for the motor-driven arrangement. Thus, the motor 1and the mechanically coupled parts thereto are omitted from theembodiment of FIG. 2 in order to maintain this diagram in simple form.In addition to the components used in FIG. 1, FIG. 2 provides for a gatecircuit 17 connected between the output of the comparator l6 and thecorresponding input of the comparator 13. Connected to the output of theinput speed sensor 11, furthermore, is a control circuit 18 forswitching the gate 17 on and off. Another gate 19 is connected in serieswith the signal line leading from the output of the comparator 13 to theinput of the regulating circuit 10. This gate 19 is controlled through aline 20 in dependence on the output signal from the comparator 16.

Once normal operating speed of the driven shaft, the gate 17 blockes thetransmission of the output signal from the comparator 16, to thecorresponding or respective input of the comparator 13. The gate 17becomes opened bythe control circuit 18 first when the signal from thesensor 11 has dropped below a predetermined value during the process instopping the driven shaft. The gate 17 in combination with the controlcircuit 18 makes it possible to fully energize the brake winding 8during a first portion of the shaft stopping process. During this firstportion of a stopping process, the difference between the output signalsfrom the sensors 11 and generator 12 is substantially large, and thebrake winding 8 is thereby to be energized independent of the outputsignal from the comparator 16. Only after the instantaneous measuredspeed of the driven shaft has dropped below a predetermined value, doesthe control circuit 18 switch on the gate 17, whereby further brakingaction becomes regulated in dependence on the speed comparison as wellas the comparison between the desired or computed brake angle and theinstantaneously measured angle. The duration of time interval duringwhich the stopping procedure for the shaft is carried out is, thereby,reduced without incurring reductions in the precision for thepositioning of the shaft.

During the stopping process for the shaft, the gate 19 is controlled sothat the output signal from the comparator 13 can be applied to theregulating circuit 10. As soon as the instantaneously measured angle ofthe shaft position agrees with the computed brake angle, so that theshaft has arrived at the desired angular position, then the blockingsignal applied by line to the gate 19 is such that the gate 19 isswitched to its blocking state. Thus, upon removal of the signal fromthe line 20, the gate 19 will not transmit. The regulating circuit 10becomes, thereby, switched off, and the two windings 7 and 8 aredeenergized. The driven shaft 4 is, as a result, disengaged from thedriving disc 3, as well as from the brake member 9, a situation which isoften advantageous. If, for example, the drive of the present inventionis used in conjunction with industrial sewing machines, then the sewingmachine shaft is released in for such an angular position sensor isshown in further detail in FIGS. 8 to 14. The input speed signalgenerator 12 provides a signal for the desired input speed of thedesired stop position and can then be further adjusted or positionedmanually as desired.

In the positioning of shafts in accordance with the species underconsideration, it is often required to move the shaft into a secondposition after it was stopped in a first position. This second positionmay be spaced from the first position by an angular amount which is lessthan 360. Thus, if the arrangement is used in conjunction again withindustrial sewing machines, and the shaft is to be stopped when theneedle is in its lowermost position, then it may be desirable to moveafterwards the needle to its uppermost position, or vice versa. In suchan operating requirement, the driven shaft, in this case, the sewingmachine shaft, is to be moved to an angle of 180 after it has attainedits first position where it is stopped through braking action. Thesecond position thereby, is a 180 displaced from the first position. Anarrangement for carrying out such a positioning operation, isschematically shown in FIG. 3. In the arrangement of FIG. 3, there aregroups of elements and components which are used in the arrangement ofFIG. 2, with the exception that no speed measuring device correspondingto the speed sensor Ill is provided in conjunction with the angularposition sensor 15. Instead, the instantaneous speed of the shaft isobtained through a differentiating stage 24 connected to the outputsignal from the angular position sensor 15. Thus, as a result ofdifferentiating the displacement Signal from the sensor 15, the speedparameter is obtained. The comparator 13 has a summing amplifier 26, p

in this arrangement of FIG. 3. A gate circuit 27, furthermore, isprovided, which is associated with the secend position or positions P2.Further gate stages 28 and 29 are associated with the first position ofthe shaft or position P1. The output of the signal generator 12 isconnected to a blocking stage or gate 30, the output of which is, inturn, connected to flip-flops 31 and 32. A monostable multivibratorcircuit 33 is connected to one output of the flip-flop 33, and an ANDgate 34 is interconnected with the elements 30, 31, 32 and 33. A timedelay circuit 35 is, furthermore, provided in the circuit diagram ofFIG. 3.

The angular position sensor 15 provides a saw-tooth voltage-signal, theamplitude of which commences to rise from an angular positioncorresponding to the position 1 of the shaft to be controlled. After theshaft executes a a rotation of 360, the saw tooth signal drops back froma maximum amplitude level to its initial value. The function of this sawtooth signal is represented in FIG. 13. A particularly advantageousdesign the driven shaft, in the form of an analogue DC voltage ofpredetermined polarity. With the use of the input speed signal generator12, it is possible to transmit simultaneously the command for thetransition from position I to the position 2 for the shaft. Such acommand for this purpose is in the form of, for example, a-DC voltage ofopposite polarity when the position to be taken into account is position2. Thus, one polarity is associated with position I and another polarityis associated with position 2.

In operation of the arrangement of FIG. 3, assumed that the shaft bedriven and then stopped in a particular position, is initially in astationary position. If, now, the input speed signal generator 12 is setin a direction so that the signal output has one predetermined polarity,then this signal will be a DC voltage having a magnitude or level whichdetermines the desired input speed for the driven shaft. This inputspeed signal from the generator 12 is transmitted through gate 30 to theinput el of the flip-flop 31. The gate 30 transmits the signal in thisphase of operation. The flip-flop 31 becomes set to the application ofthis signal to the input el, and transmits, thereby, a signal throughline 38, to the gate 19 so as to switch this gate 19 for transmittingthe output from the summing amplifier 26 to the regulating circuit 10.Ths flip-flop 32 has also applied to it the signal output from the gate30, and provides, in turn, an output signal through the line 40, forswitching gate 29 whereby this gate 29 will not transmit. As a result,no signal can be transmitted to the summing amplifier 26, from thecircuit or gate 27 corresponding to position P2 of the shaft. The gate28 associated with the first position of the shaft or F1 is free totransmit as a result of the signal on the line 41, but this has noeffect upon the functional operation, since gate 17 is inhibited fromtransmitting its signal input.

The input speed signal from the device 12 is applied, furthermore,through the summing amplifier 26.Since the shaft, to be positioned, isstill stationary, the instantaneous speed signal as derived from thedifferentiating network 24, and applied to the summing amplifier 26, iszero. The resultant output signal from the summing amplifier 26 isapplied, through the gate 19, to the regulating circuit 10 andinfluences the latter whereby the coupling winding 7 is energized. Thedriven shaft 4 becomes, thereby, coupled to the shaft 2 of the motor,and the driven shaft 4 is, consequently, accelerated.

The input speed signal from the device 12 furthermore, inhibits thetransmission of gate 117, simultaneously through the application of asignal to line 39,

whereby the output signal from the comparator 16 is prevented fromreaching the comparator 13. The comparator 16 is also constructed in theform of a summing amplifier.

For every revolution of the driven shaft 4, the angular position sensor15 provides a linearly increasing voltage from a minimum value to amaximum value. The slope of this linear function or the rate of increasein value of this function is, determined through differentiation by thedifferentiating stage 24 and the output signal from this stage 2drepresents the actual. instantaneous output speedof the shaft 4. Thisactual output speed of the shaft 4 is compared with the desired inputspeed in the summing amplifier 26. As soon as the output signal from thesumming amplifier 26 indicates that the difference between the actualoutput speed and the desired input speed is zero, then the desired inputspeed is obtained and the regulating circuit 10 will deenergize thewinding 7. The summing amplifier 26 causes the regulating circuit 10 tomaintain the driven shaft 4 at the desired input speed. In the case thatthe input speed signal generator 12 is set to the new input speed value,then the summing amplifier 26 and regulator l combine to operate so asto adjust the speed of the driven shaft 4 to the new value.

The positioning of the driven shaft at the position P1, or the firstposition, is attained by setting the input speed signal generator 12 tozero. With this setting, the blocking signal applied to the line 39 isremoved. The gate '17, however, remains still in an untransmittingstate, temporarily, as a result of the infuence of the gate controlcircuit 18. Thus, the signal from the amplifier 16 is still blocked frombeing transmitted by the gate 17, as a result of the control circuit 18.As a result, the summing amplifier 26 receives only the relatively highsignal indicating the output instantaneous speed of the shaft 4, whereasthe input speed signal is zero. The regulator circuit 10, therebyapplies full energization to the brake winding 8. Consequently, thedriven shaft becomes subjected to maximum braking moment, independent ofthe output signal from the comparator 16, so that the driven shaft 4becomes strongly braked. When the output instantaneous speed of theshaft corresponds to the predetermined level, the control circuit 18becomes switched and as a result, the gate 17 is permitted to transmitthe signal from the comparator 16.

Through the gate 28 associated with the first stop position of the shaft4, the difference signal from the com parator 16 is transmitted to thesumming amplifier 26. As a result, the difference signal between thedesired input angular position and the actual instantaneous output shaftposition is superimposed upon the speed signals for the input and outputshaft speeds, and this superimposing of the position signals upon thespeed signals in this manner, causes attenuation or decrease in theexcitation of the braking winding. Further braking action, thereby, isapplied in a regulated manner as a function of angular position, inaccordance with the computed braking function provided by the circuit14. As soon as the output speed signal and the output signal from thecomparator 16 are both zero, then the position P1 for the driven shaft 4is attained, and the shaft is held stationary.

The circuit 35 is designed so that it provides an output signal when itsinput corresponds to the instantaneous actual angular position of theshaft which is greater than'that for a predetermined time interval. Thistime interval is determined so that the circuit 35 will not becomeactivated when the position P1 is passed through during rotation of theshaft 4 while under speed, as well as during braking. However, after theshaft has become stationary in the position P], then the circuit 35becomes actuated. With actuation of this circuit 35, a signal istransmitted from the circuit to the input e2 of the flip-flop 31. Thiscauses the flip-flop 31 to be reset, whereby the gate 19 is inhibitedfrom transmitting through the line 38. The regulating circuit becomes,thereby, disconnected from the comparator 13. As a result, the couplingand brake windings 7, 8 are de-energized. The driven shaft 4 can,thereafter, be manually rotated as desired.

1f the speed signal generator 12 is set to the opposite direction, asignal of opposite polarity is applied to the flip-flop 32, by way ofthe gate 30. The flip-flop 32 becomes thereby switched, and actuates themonostable multivibrator circuit 33 with the signal applied from theoutput A1 of the flip-flop 32. With the consequent switching of themonostable multivibrator circuit 33, the latter provides an outputsignal for a time interval which is larger than the time duration whichis required for moving the driven shaft 4 from position 1 into position2. This output signal from the multivibrator 33 is applied to theflip-flop 31 at input c3, and the gate 19 is permitted to transmit, as aresult of the signal upon line 38. At the same time, the gate 30 isswitched so as to prevent transmitting of its signal from the device 12,as a result of the line 42, so that no signal from the speed generator12 can reach the comparator 13. The signal from the output A1 of theflip-flop 32 permits the gate 29 associated with position P2, totransmit as a result of this signal on line 40. The transmitting stateof the gate 28 associated with position P1 is continued. The summingamplifier cannot receive any signal from the comparator 16 thereby.

The circuit gate 27 associated with position P2, compares theinstantaneous output angular position of the shaft 4, as indicated bythe sensor 15, with a reference voltage U As long as the actual positionof the shaft 4 as represented by the signal from the sensor 15, issmaller than this reference voltage, the comparator 13 receives a signalby which the coupling winding 7 becomes energized. The driven shaft 4commences, thereby to rotate anew. As soon as the angular positionsignal from the sensor 15 becomes equal to the value of the referencevoltage U,,, this gate circuit 27 transmits, through the gate 29, to thesumming amplifier 26 a signal which when transmitted through gate 19applies a braking commence signal to the regulator 10. As a result, theshaft 4 becomes braked and is held stationary in position P2.

As soon as the monostable multivibrator circuit 33 is returned to itsstable state, the flip-flop 31 becomes reset. The gate 19 becomes,thereby switched to the state where it does not transmit, and theregulating circuit 10 is disconnected from the output of the summingamplifier 26. Consequently, both windings 7 and 8 are deenergized. Toprepare for a new operating cycle, the signal inhibiting states of thegates 28 and 30 must be discontinued so that these two gates are free totransmit. The gate 29 associated with position P2, becomes againswitched so that it will not transmit or it is in the inhibiting state.

The AND gate 34 makes certain that the flip-flop 32 becomes switchedfirst after the shaft 4 is held stationary in the position Pl. Throughthis condition, it is achieved that the positioning of the shaft into aposition P2 must always be preceded by a positioning of the shaft into aposition P1.

As illustrated by equations 1 to 4 above, a quadratic relationshipprevails between the brake angle and the speed of the shaft whenconstant braking torque is applied. This quadratic relationship,however, is relatively complicated from the circuit point of view. Thus,it is relatively involved to mechanize this equation in circuit 4. Thequadratic function can be approximated through w e' C The precedingequation 5 can be reproduced in circuit form through the use of anoperational amplifier 45 with feedback, as shown in FIG. 4. A germaniumdiode when driven in the conductive state, has an output function whichis proportional to the logarithm of the current through the diode, minusthe logarithm of the saturation current. By makinguse of thischaracteristic of the diode, the feedback network 46, shown in FIG. 4can be constructed inaccordance with making use design illustrated inFIG. 5. Thus, the feedback circuit 46 can consist of a resistor 48connected between the output and input of the operational amplifier 45,and a germanium diode 48 connected between the output of the amplifierand ground potential.-

The differentiation process carried out by the circuit 24 fordifferentiating the actual output angular position of the shaft 4, canalso be approximated in an advantageous manner. Direct differentiationcan easily lead to instabilitiesin the regulating circuit. Thus, it canbe easily shown that the equation y(t) dx/dt can be expressed in theform of y x by I y dt I when b is not equal to 1. Equation 7 can beproduced through two operational amplifiers in accordance with.

the arrangement of FIG. 6. The first amplifier 49 in FIG. 6, is arrangedas a summing amplifier, whereas the second amplifier 50 is designed asan integrator. The

schematic arrangement of FIG. 6 may -be obtained through the detaileddescription of the circuit diagram of. FIG. 7.

For reliable operation of the circuit arrangements of FIGS. 1, 2 and 3,it is particularly important to obtain precisely'the actual outputposition of the shaft 4. As a result, the angular position sensor has aparticularly important part in the arrangement. From the viewpointof'operating reliability and high operating life, it is desirable thatthe angular position sensor be of the contactless type. Such a device15, furthermore, should be capable of providing a precisely andreproducable analogue voltage for each possible angular position of theshaft, independent of the prevailing speed of the shaft. An angularposition sensor of this type which meets these requirements, is shown inFIGS. 8 to 12. The sensor has a rotational member or body 60 which ismounted on one end of the shaft 4, not shown in FIG. 8. The rotationalmember 60 is held to the shaft 4 through a set screw which is threadedin a bore 61 of the member 60. A ball bearing 62 is mounted upon aportion of the body 60 which has a smaller diameter, and is locatedtowards the right in the drawing of FIG. 8. The outer ring of the ballbearing 62 is seated in a stationary part of a housing 63. A measuringhead 65, furthermore, is secured by means of screws 64 to the housingportion 62.

lid

end portions 73, 74 of two magnetic conductive measuring strips 75, 76.These measuring strips 75, 76 are mounted adjacent to each other in aradial manner relative to the axis of the shaft 4 or the rotationalmember 60. The angled element or bracket 66 carries a U- shaped outerscreening member 78, as well as an oppositely-lying U-shaped interiorscreening member 79. The interior screening member is oriented withrespect to the outer scanning member 78 by the amount of 90. The widthof the interior screening member corresponds essentially to theoppositely lined outer edges of the measuring strips 75, 76.

In the space between the ends of the outer screening 78, on the onehand, as well as the ends of the inner screening 79 and the measuringstrips 75, 76, on the other hand, are two pole pieces or elements 80,81. These pole pieces are clamped, through a screw 82, between aninsulating element 83 or 841 and a magnetically conductive ring 85 or86. These pole pieces, furthermore, rotate together with the rotationalmember 60 and thereby together with the shaft 4 to be regulated inmovement. Between the rings 85, 86 is a ring-shaped permanent magnet 87which is axially polarized. The pole pieces 80, 81 are of this shaftillustrated in FIG. 9. Their outer edge, as shown in that FIG. 9 form aspiral which satisfies the condition that dw/dr const.

where r is the radiusof the spiral.

The rings 85, 86 form an enclosure for the magnet 87, which preventsthat the pole pieces 80, 811 become saturated. These rings 85, 86,furthermore, reduce strongly the stray magnetic flux and determine thefield strength or field intensity at the pole pieces through theirdefined magnetic reluctance. Through the use of the hall generator 72and the measuring strips 75, 76 the magnetic flux is measured betweenthe pole pieces 80, 8l'within the region of the measuring strips 75, 76.In view of the shape of the'pole pieces, as shown in FIG. 9, thismagnetic flux and thereby the voltage provided by the hall generator 72,are proportional to the angu- .lar rotation of the shaft 4 which istransmitted directly to the rotational member 60. At the output of thehall generator, therefore, a voltage is available as shown in FIG. 13.It may be seen, thereby that by adjusting the angular position of therotational member 60 in relation to the shaft 4,-the desired input angle(which corresponds to position P11 in accordance with FIG. 3) may beobtained in a predetermined and simple manner.

The input speed signal generator 13 can be designed directly on thebasis of the arrangement described above in conjuntion with the angularposition sensor 15, with the exception that the rotational member 60 isnot connected to the driven shaft 4. In this case, the rotational member60 is instead to be connected to a positioning member or element whichis actuated or adjusted manually by being set either by hand or by foot.A further input speed signal generator for the device 12 is also wellknown in the art in the form of a device which operates on thecontactless principle.

FIG. 14 shows the hall generator for measuring angular position throughthe sensor 15, when connected with a stabilizing circuit which improvesparticularly upon the desired angular input position signalling, withinthe frame of the present invention. In this arrangement, the sensor 15is in the form of the construction illustrated by FIGS. 8 to 12.

As already mentioned above, the angular position sensor 15 provides alinearly increasing saw-tooth voltage from a lowest level U,, to amaximum level U,. Through the circuit arrangement shown in FIG. 14, thevoltage values corresponding to U and U as, for example, zero volts and+6 volts, respectively, are held constant. Values between these twoextreme limits are also thereby precisely determined. For this purposeof maintaining constant the limit voltages, the output signal from theoperational amplifier 90 is applied to integrators with substantiallylarge time constants. These integrators consist essentially of aresistor 91, a diode 92, and a capacitor 93 for one network, and a diode94 and capacitor 95 for another network. The output voltages from theintegrators are compared wth reference voltages of which one consist ofground potential and the other is determined by a Zener diode 96.Through the regulated variation of the voltage value of U theoperational amplifier 90 becomes correspondingly influenced through thetransistors 97, 98 and a resistor 99. The operational amplifier becomesinfluenced by a corresponding variation of the operating point of theamplifier. The regulated variation of the voltage value U, varies thehall generator current, through transistors 100, 101 and 102. If, forexample, a positive voltage appears across the diode 94 during a longertime interval, then this implies that the amplification is too low. As aresult, the hall generator current is increased by way of the threetransistors 100, 101, 102. The arrangement in accordance with FIG. 14allows the elimination of all temperature and component manufacturingvariations.

In accordance with a modified embodiment of the the present invention,the actual output speed of the shaft 4 can also be determined throughthe use of a speed measuring tachometer. Such a tachometer, for example,has a permanent magnetic disc connected to the driven shaft 4. Thepermanent magnetic disc has a peripheral surface of an alternatingsequence of magnetic North and South poles. A magnetic coil is locatedin proximity of the permanent manetic disc and has induced within it avoltage, the amplitude and frequency of which, are essentiallyproportional to the rotational speed of the driven shaft 4.

In such a case, the actual ouput angular position of the shaft can bederived from the measured speed through the tachometer, ortachogenerator, by applying the speed signal to an integrator orintegrating stage. Such an integrating stage sums the pulses from thetachogenerator. The integrator becomes reset through a synchronizerduring each rotation of the shaft 4, in correspondence to apredetermined, desired stopped position of the shaft 4. Thesynchronizer, for this purpose is well known in the art. The advantageof a speed tachometer or tachogenerator resides on the basis that asubstantially high output voltage can be derived without noise effects,which can be applied directly as the actual output value, to theregulator circuit 10. Through the use of a synchronizer in accor-' dancewith the conventional design, a reproducable voltage signal can beobtained from the hall generator for the desired input position for theshaft, for each revolution of the shaft.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofmethods and means for positioning angular shafts, differing from thetypes described above.

While the invention has been illustrated and described as embodied in amethod and means for positioning angular shafts, it is not intended tobe limited to the details shown, since various modifications andstructural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

I claim:

1. A method for moving a shaft to a predetermined angular position,comprising the steps of: applying a source of rotary motion to saidshaft for rotating said shaft at an angular speed corresponding to thespeed of said source; measuring the instantaneous angular speed of saidshaft; computing from the instantaneous speed of said saft a brakingangle throughout which said shaft is to be braked to stop said shaft atsaid predetermined angular'position, said braking angle being dependenton said instantaneous speed; removing said source of rotary motion fromsaid shaft and permitting said shaft to continue rotating withoutcontinued application of said source; comparing the instantaneousangular position of said shaft with said braking angle; comparing saidinstantaneous speed of said shaft with a predetermined desired speed;and braking said shaft dependent on said comparing steps so that saidshaft becomes stopped at said predetermined angular position.

2. The method as defined in claim 1, wherein said braking of said shaftis fully applied initially and is applied partially thereafter forbringing said shaft to a stopped position at said predetermined angularposition.

3. The method as defined in claim 2, wherein the braking interval duringwhich braking is fully applied is expressed as w =f (n), the intervalduring which partial braking is applied being expressed by w f,(n),wherein w is the angular shaft position relative to said predeterminedangular position and n is said instantaneous angular speed of saidshaft, the instant of changing from fully applied braking to partialbraking corresponding to the intersection of f,(n) and f,(n).

4. The method as defined in claim 1, wherein said instantaneous angularspeed of said shaft is'derived from the instantaneous angular positionof said shaft.

5. The method as defined in claim 1, wherein the instantaneous angularposition of said shaft is derived from said instantaneous angular speedof said shaft, said instantaneous angular speed of said shaft beingdefined by a sequence of pulses, said instantaneous angular position ofsaid shaft being defined by a summation of said pulses.

6. The method as defined in claim 1, including the step of removing saidbraking from said shaft when said shaft has attained said predeterminedangular position.

7. An arrangement for carrying out the method of claim 1 for moving ashaft to a predetermined angular position, comprising, in combination, asource of rotational motion for rotating said shaft at an angular speedcorresponding to the speed of said source; coupling means between saidsource and said shaft; braking means connectable to said shaft forbraking said shaft and decreasing the speed of said shaft, said brakingmeans being applied to said shaft when said shaft is decoupled from saidsource; speed measuring means connected to said shaft for measuring theinstantaneous speed of said shaft; first comparator means connected tosaid speed measuring means for comparing said instantaneous speed with adesired input speed of said shaft; computing means connected to saidspeed measuring meas for computing a braking angle function; secondcomparator means connected to said computing means for comparing abraking angle function with said predetermined angular function; andregulating means connected to said comparator means for regulating saidbraking means in dependency on said braking angle function, whereby saidshaft is braked so that said shaft is stopped at said predeterminedangular position.

8. The arrangement as defined in claim 7, wherein the output of saidsecond comparator means is connected to one input of said firstcomparator means.

9. The arrangement as defined in claim 8, including signal gating meansconnected in series with the output of said second comparator means;gate control means connected to said gating means and said speedmeasuring means for controlling the transmission of said gating means sothat the output of said second comparator means is not transmitted tosaid first comparator means when said instantaneous speed ofsaid shaftexceeds a predetemined value.

10. The arrangement as defined in claim 8, including speed input meansfor applying a desired input speed to said first comparator means;signal gating means connected in series with the output of said secondcomparator means, said gating means being controlled by said input speedmeans so that the output of said second comparator means is nottransmitted to said first comparator means when the input speed appliedby said input speed means is different from zero.

11. The arrangement as defined in claim 7, including gating meansconnected in series with the input to said regulating means fordisconnecting said coupling means and said braking means from said shaftin dependency on the arrival of said shaft at said predetermined angularposition.

, said speed measuring means comprises speed computing means forcomputing the instantaneous speed of said shaft from the angularposition of said shaft.

14. The arrangement as defined in claim 13, wherein said speed computingmeans for computing said instantaneous speed of said shaft comprises twooperational amplifiers connected in series, one of said operationalamplifiers being a summing amplifier and the other one of saidamplifiers being an integrating amplifier, said two amplifiers beingfurther connected so that when applying an input signal of the form x(t)to said summing amplifier the output signal of said summing amplifier isof the form of y(t) x by I y dt.

15. The arrangement as defined in claim 7, wherein said computing meanscomprises an operational amplifier with feedback network interconnectedto said operational amplifier so that upon applying an input signal ofthe form of x(t) to the input of said operational amplifier, an outputsignal from said amplifier is obtained in the form of y(t) e C.

16. The arrangement as defined in claim 7, wherein said secondcomparator means comprises an operational amplifier with feedbacknetwork whereby said operational amplifier functions as a summingamplifier.

17. The arrangement as defined in claim 7, wherein said first comparatormeans comprises an operational amplifier with feedback networkinterconnected to said operational amplifier, whereby said operationalamplifier functions as a summing amplifier.

18. The arrangement as defined in claim 7, including angular positionsensing means for sensing the instantaneous angular position of saidshaft; control means connected to said angular position sensing meansand to said regulating means for moving said shaft to a secondpredetermined angular position after having attained said firstmentioned predetermined angular shaft position.

19. The arrangement as defined in claim 18, including gating meansconnected to said control means and output of said second comparatormeans for altematingly blocking and transmitting the signal outputs ofsaid control means and said second comparator means.

20. The arrangement as defined in claim 19, including programming meansconnected to said gating means for controlling said gating means so thatthe positioning of said shaft to a second predetermined angular positionis always preceded by braking said shaft to said first-mentionedpredetermined angular position.

21. The arrangement as defined in claim 18, includ ing input speedapplying means for applying said desired input speed of said shaft, thesignal output from said input speed applying means signalling also thetransition from said first mentioned predetermined angular to a secondpredetermined angular position.

22. The arrangement as defined in claim 21, including gating meansconnected between said input speed applying means and said regulatingmeans for inhibiting the transmission of the output signal from saidinput speed applying means to said regulating means during the intervalwhen said shaft moves from said firstmentioned predetermined angularposition to said second predetermined angular position.

23. The arrangement as defined in claim 12, including a source ofreference voltages for comparing the minimum and maximum output voltagevalues from said hall generator means; and auxiliary regulating meansconnected to said hall generator means for regulating said minimum andmaximum output voltages 26. The arrangement as defined in claim 7,wherein said coupling means comprises an electromagnetic coupling havingan actuating winding energized by said regulating means.

27. The arrangement as defined in claim 7, wherein said braking meanscomprises an electromagnetic brake having a winding energized by saidregulating means.

1. A method for moving a shaft to a predetermined angular position,comprising the steps of: applying a source of rotary motion to saidshaft for rotating said shaft at an angular speed corresponding to thespeed of said source; measuring the instantaneous angular speed of saidshaft; computing from the instantaneous speed of said saft a brakingangle throughout which said shaft is to be braked to stop said shaft atsaid predetermined angular position, said braking angle being dependenton said instantaneous speed; removing said source of rotary motion fromsaid shaft and permitting said shaft to continue rotating withoutcontinued application of said source; comparing the instantaneousangular position of said shaft with said braking angle; comparing saidinstantaneous speed of said shaft with a predetermined desired speed;and braking said shaft dependent on said comparing steps so that saidshaft becomes stopped at said predetermined angular position.
 2. Themethod as defined in claim 1, wherein said braking of said shaft isfully applied initially and is applied partially thereafter for bringingsaid shaft to a stopped position at said predetermined angular position.3. The method as defined in claim 2, wherein the braking interval duringwhich braking is fully applied is expressed as w f1(n), the intervalduring which partial braking is applied being expressed by w f2(n),wherein w is the angular shaft position relative to said predeterminedangular position and n is said instantaneous angular speed of saidshaft, the instant of changing from fully applied braking to partialbraking corresponding to the intersection of f1(n) and f2(n).
 4. Themethod as defined in claim 1, wherein saId instantaneous angular speedof said shaft is derived from the instantaneous angular position of saidshaft.
 5. The method as defined in claim 1, wherein the instantaneousangular position of said shaft is derived from said instantaneousangular speed of said shaft, said instantaneous angular speed of saidshaft being defined by a sequence of pulses, said instantaneous angularposition of said shaft being defined by a summation of said pulses. 6.The method as defined in claim 1, including the step of removing saidbraking from said shaft when said shaft has attained said predeterminedangular position.
 7. An arrangement for carrying out the method of claim1 for moving a shaft to a predetermined angular position, comprising, incombination, a source of rotational motion for rotating said shaft at anangular speed corresponding to the speed of said source; coupling meansbetween said source and said shaft; braking means connectable to saidshaft for braking said shaft and decreasing the speed of said shaft,said braking means being applied to said shaft when said shaft isdecoupled from said source; speed measuring means connected to saidshaft for measuring the instantaneous speed of said shaft; firstcomparator means connected to said speed measuring means for comparingsaid instantaneous speed with a desired input speed of said shaft;computing means connected to said speed measuring meas for computing abraking angle function; second comparator means connected to saidcomputing means for comparing a braking angle function with saidpredetermined angular function; and regulating means connected to saidcomparator means for regulating said braking means in dependency on saidbraking angle function, whereby said shaft is braked so that said shaftis stopped at said predetermined angular position.
 8. The arrangement asdefined in claim 7, wherein the output of said second comparator meansis connected to one input of said first comparator means.
 9. Thearrangement as defined in claim 8, including signal gating meansconnected in series with the output of said second comparator means;gate control means connected to said gating means and said speedmeasuring means for controlling the transmission of said gating means sothat the output of said second comparator means is not transmitted tosaid first comparator means when said instantaneous speed of said shaftexceeds a predetemined value.
 10. The arrangement as defined in claim 8,including speed input means for applying a desired input speed to saidfirst comparator means; signal gating means connected in series with theoutput of said second comparator means, said gating means beingcontrolled by said input speed means so that the output of said secondcomparator means is not transmitted to said first comparator means whenthe input speed applied by said input speed means is different fromzero.
 11. The arrangement as defined in claim 7, including gating meansconnected in series with the input to said regulating means fordisconnecting said coupling means and said braking means from said shaftin dependency on the arrival of said shaft at said predetermined angularposition.
 12. The arrangement as defined in claim 7, including a hallgenerator for measuring the instantaneous position of said shaft, saidhall generator having a magnetic disc coupled to said shaft, saidmagnetic disc having a varying radius from a predetermined minimumradius to a predetermined maximum radius, the transition between saidminimum radius and said maximum radius being a step function.
 13. Thearrangement as defined in claim 7, wherein said speed measuring meanscomprises speed computing means for computing the instantaneous speed ofsaid shaft from the angular position of said shaft.
 14. The arrangementas defined in claim 13, wherein said speed computing means for computingsaid instantaneous speed of said shaft comprises two operationalamplifiers connected in series, one of said operationaL amplifiers beinga summing amplifier and the other one of said amplifiers being anintegrating amplifier, said two amplifiers being further connected sothat when applying an input signal of the form x(t) to said summingamplifier the output signal of said summing amplifier is of the form ofy(t) x + by - Integral y dt.
 15. The arrangement as defined in claim 7,wherein said computing means comprises an operational amplifier withfeedback network interconnected to said operational amplifier so thatupon applying an input signal of the form of x(t) to the input of saidoperational amplifier, an output signal from said amplifier is obtainedin the form of y(t) ex + C.
 16. The arrangement as defined in claim 7,wherein said second comparator means comprises an operational amplifierwith feedback network whereby said operational amplifier functions as asumming amplifier.
 17. The arrangement as defined in claim 7, whereinsaid first comparator means comprises an operational amplifier withfeedback network interconnected to said operational amplifier, wherebysaid operational amplifier functions as a summing amplifier.
 18. Thearrangement as defined in claim 7, including angular position sensingmeans for sensing the instantaneous angular position of said shaft;control means connected to said angular position sensing means and tosaid regulating means for moving said shaft to a second predeterminedangular position after having attained said first mentionedpredetermined angular shaft position.
 19. The arrangement as defined inclaim 18, including gating means connected to said control means andoutput of said second comparator means for alternatingly blocking andtransmitting the signal outputs of said control means and said secondcomparator means.
 20. The arrangement as defined in claim 19, includingprogramming means connected to said gating means for controlling saidgating means so that the positioning of said shaft to a secondpredetermined angular position is always preceded by braking said shaftto said first-mentioned predetermined angular position.
 21. Thearrangement as defined in claim 18, including input speed applying meansfor applying said desired input speed of said shaft, the signal outputfrom said input speed applying means signalling also the transition fromsaid first mentioned predetermined angular to a second predeterminedangular position.
 22. The arrangement as defined in claim 21, includinggating means connected between said input speed applying means and saidregulating means for inhibiting the transmission of the output signalfrom said input speed applying means to said regulating means during theinterval when said shaft moves from said first-mentioned predeterminedangular position to said second predetermined angular position.
 23. Thearrangement as defined in claim 12, including a source of referencevoltages for comparing the minimum and maximum output voltage valuesfrom said hall generator means; and auxiliary regulating means connectedto said hall generator means for regulating said minimum and maximumoutput voltages from said hall generator means in dependence on saidreference voltages.
 24. The method as defined in claim 1, including thestep of applying a braking torque to said shaft while braking saidshaft, said braking torque being below the maximum braking torqueapplicable to said shaft when braking said shaft in dependence on saidbraking angle.
 25. The arrangement as defined in claim 7, wherein saidsource of rotational motion is an electrically driven motor.
 26. Thearrangement as defined in claim 7, wherein said coupling means comprisesan electromagnetic coupling having an actuating winding energized bysaid regulating means.
 27. The arrangement as defined in claim 7,wherein said braking means comprises an electromagnetic brake having awinding energized by said regulatIng means.